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I Can't Wait Well You Shouldn't Have To

You’re waiting for another team to load the database

This problem derives from recent consulting work. It has been changed to protect the innocent.

Problem: Database synchronization takes about 10 hours.

A Few facts

• Currently convert roughly 2 records per second
• As written, running tests requires another team to load records in to an external database.
• Think wait-time is roughly 300 – 400 ms per record (reading and writing)

Final Results: 15 threads, 28 minutes…

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Here's the code as written (not test first)

public void execute() {
   service = Executors.newFixedThreadPool(THREADS);
 
   for (Long id : vendorSynchronizationService.getVendorIds()) {
      final Long finalId = id;
      service.execute(new Runnable() {
         public void run() {
            vendorSynchronizationService.synchronizeRecord(finalId);
         }
      });
   }
   service.shutdown();
}

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Create a Fake Vendor Synchronization Service

First the test:

public class FakeVendorSynchronizationServiceTest {
   @Test
   public void convertsApproximately2PerSecond() throws Exception {
       VendorSynchronizationService service = 
           new FakeVendorSynchronizationService();
 
       long start = System.currentTimeMillis();
 
       service.synchronizeRecord(0);
       service.synchronizeRecord(0);
 
       long stop = System.currentTimeMillis();
       long runningTime = stop - start;
 
       assertTrue("" + runningTime, 
          runningTime >= 900 && 
          runningTime <= 1100);
    }
}

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Create a Fake Vendor Synchronization Service

Next, the fake:

public class FakeVendorSynchronizationService 
                                extends VendorSynchronizationService {
 
   public void synchronizeRecord(long recordId) {
      simulateDatabaseReadDelay();
      simulateWorkLoad();
   }
 
   private void simulateDatabaseReadDelay() {
      try { Thread.sleep(450); } 
      catch (InterruptedException ignored) { ; }
   }
 
   private BigDecimal simulateWorkLoad() {
      BigDecimal value = new BigDecimal(0);
      for (int i = 0; i < 200000; ++i)
         value = value.multiply(new BigDecimal(1023));
      return value;
   }
}

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Next, express how fast is fast enough

public class VendorSynchronizerTest {
   private static final int DELAY = 60;
 
   @Test(timeout = DELAY * 1000)
   public void CanProcess120VendorsIn60Seconds() throws Exception {
      FakeVendorSynchronizationService service 
         = new FakeVendorSynchronizationService();
      VendorSynchronizer synchronizer 
         = new VendorSynchronizer(service);
 
      synchronizer.execute();
 
      synchronizer.service.awaitTermination(DELAY, TimeUnit.SECONDS);
 
      assertTrue(synchronizer.service.isTerminated());
    }
}

As a bonus, this validates MT logic as well…

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